This proposed research program is a direct extension of our earlier program with the same fundamental goals: the investigation of reproduction, oogenesis and early embryonic development and the molecular mechanisms that control genetic activity. A variety of methods and living systems continue to be utilized with emphasis on the sea urchin embryo. Nucleic acid sequence comparison by hybridization is a central method. Its usefulness and specificity have been greatly improved by the use of several libraries of sea urchin recombinant DNA fragments. We will continue to investigate the sequence characteristics of RNA synthesized during oogenesis and stored in the egg and the RNA synthesized during development, both hnRNA and polysomal messenger RNA. Recent work on transcripts of individual families of repetitive sequences which are highly represented in RNA is to be extended. The modulation in concentration of many of these transcripts by factors of at least a hundred after fertilization and during development indicates that they play a crucial role. The modulation of populations of messenger RNA has been observed and will be followed up by examining the history of individual messages and their production during oogenesis as well as later, in development. These measurements are aimed at understanding the mechanism of gene regulation and the determinants of morphogenesis. Specific tests are being carried out to determine the role of the repetitive sequences adjacent to structural genes and their transcripts in cellular RNAs. Studies are also planned of the cytoplasmic localization of molecules implicated in the regulatory processes. We plan to examine the ways in which the system of regulation establishes the process of oogenesis, morphogenesis and the time course of development.